1. Field of the Invention
The present invention relates generally to designing and manufacturing contact lens eyewear and more specifically to a method for fitting contact lenses.
2. Description of the Related Art
Optical enhancement devices and refractive surgery are two techniques used to correct vision. One reason to correct vision is due to myopia, also referred to as nearsightedness. Refractive surgery may include radial keratotomy and photorefractive keratotomy. Optical enhancement devices may include contact lenses and glasses. Contact lenses are prescribed to correct refractive errors in vision. Optical enhancement devices may still be used after refractive surgery if there is still some nearsightedness. Contact lenses include soft contact lenses and rigid gas permeable contact lenses. Rigid gas permeable contact lenses are examples of hard contact lenses.
Rigid gas permeable lenses may be more durable than soft contacts and better for correcting astigmatism than soft contacts. Further, the shape of the rigid gas permeable lens may be modified as opposed to soft contacts, and require less maintenance than soft contacts. One method currently used to fit rigid gas permeable lenses involves weeks of trying various shapes for the rigid gas permeable lens using experimental fitting techniques.
To fit rigid gas permeable lenses, the optometrist or other person performing the fitting may apply fluorescein dye drops to the eyes of the patient to reveal the amount of clearance, or distance, between the rigid gas permeable lens and the corneal surface. Fluorescein is a bright orange dye that fluoresces with a color that is lime green in the presence of cobalt blue light. In the fitting process, as more clearance is present between the rigid gas permeable lens and the cornea, more dye accumulates in the clearance. This increase in accumulation is indicated by a fuller green fluorescence of the dye. The fluorescein test is considered reliable but is not usable with the popular soft contact lenses because the material used in soft contact lenses. These materials often include hydrogel, which absorbs the fluorescein dye. As a result the soft contact lens becomes stained.
A fluorescein pattern showing the rigid gas permeable lens with even clearance between the rigid gas permeable lens and the eye along the cornea of the eye with only slight tear pooling between the lens and cornea may be considered a good fit. Tear pooling is indicated by the amount of fluorescein that accumulates.
During a fitting, after the optometrist has applied the fluorescein drops, an evaluation of the tear pooling indicates what type of correction to the rigid gas permeable lens may be made, if a correction is made. Different types of tear pooling patterns may indicate different correctional steps. Correctional steps on a new design of the rigid gas permeable lens may be made, for example, by making changes to the base curve radius, overall diameter, optical zone diameter, secondary curve radius, peripheral curve radius, and/or center thickness.
Current methods for fitting rigid gas permeable lenses often involve many sessions to perform fittings with the optometrist evaluating the fluorescein and tear pooling to make correctional steps in each session. The correctional steps are used to create a new design for the rigid gas permeable lens. After each new design, another session for a fitting may be performed and that session may result in yet another new design. It would be useful to provide a method of fitting rigid gas permeable lenses which decreases the number of fitting sessions.
The method of fitting using trial lenses is a long and laborious process, and can be very expensive if the rigid gas permeable lenses are difficult to manufacture. Additionally, arriving at a precise fit can require many weeks or months using many different trial rigid gas permeable lenses. During this time the patient does not have use of the desired or needed rigid gas permeable lens.
Accordingly, it would be advantageous to have a method and apparatus, which takes into account one or more of the issues discussed above as well as possibly other issues.